Guidewires are widely used in medical procedures. Vascular guidewires, for example, are commonly used to guide catheters through tortuous vasculature to distal sites. By way of example but not limitation, a guidewire used for delivering coronary stents might enter the patient's body down at the femoral artery, traverse the intervening vasculature, and terminate in a coronary artery. An orthopedic arthroscopic guidewire, on the other hand, is commonly used to guide tools and/or implants through a keyhole incision and down to an internal surgical site, where the tools and/or implants are to be utilized.
The present invention is directed to vascular guidewires and the like, among other things.
Due to their application, vascular guidewires generally require different properties for different portions of the guidewire.
More particularly, the distal end of the guidewire generally requires higher elasticity and lower stiffness, in order to provide sufficient flexibility to navigate through highly tortuous anatomy. At the same time, the distal end of the guidewire still requires some stiffness, in order to maintain the torque transmission requirements of the guidewire and to provide sufficient support for stent delivery.
The proximal end of the guidewire generally requires lower elasticity and higher stiffness, in order to provide sufficient column strength to ensure adequate pushability of the guidewire through substantial vascular lengths and in order to provide adequate torque transmission along the guidewire. At the same time, the proximal end of the guidewire still requires some flexibility, in order to permit the guidewire to navigate through highly tortuous anatomy.
Due to the varying demands on various parts of the guidewire, it is generally desirable to utilize different materials to form different parts of the guidewire. Thus, in recent years, several types of “composite” guidewires have been developed. These composite guidewires are generally formed by joining two wire lengths, each wire length being made from a different material having different intrinsic properties. Typically, these composite guidewires utilize (i) stainless steel wire to form the proximal end of the guidewire, and (ii) nickel titanium (i.e., Nitinol) wire to form the distal end of the guidewire. By abutting these two different wire segments into a single contiguous guidewire, the properties of stainless steel (e.g., lower elasticity and higher stiffness) are provided at the proximal end of the composite guidewire, and the properties of nickel titanium (e.g., higher elasticity and lower stiffness) are provided at the distal end of the composite guidewire. Thus, superior pushability and torquability are provided in the proximal segment of the composite guidewire, and flexibility, durability and support are provided in the distal segment of the composite guidewire.
One consequence of replacing conventional, single-segment guidewires with composite, multi-segment guidewires is the introduction of a joint between adjoining segments of the composite guidewires. This joint can be problematic, inasmuch as it is imperative that the joint not undermine the integrity of the guidewire. In other words, it is important that the joint provide adequate (i) tensile strength, (ii) torque strength, (iii) bending moment performance, and (iv) failure mode characteristics, among other things. By way of example but not limitation, tensile strength is important since, if the guidewire becomes stuck during use, it may be necessary to pull the guidewire free.
In the prior art, a cylindrical coupler has generally be used to join together two wire segments each having circular cross-sections.
For example, U.S. Pat. No. 5,341,818 (Abrams et al.) discloses a connector made of Nitinol tubing which compresses inwardly onto the two wire segments so as to secure the joint.
U.S. Pat. No. 5,980,471 (Jafari) discloses a tubular connector which provides a mechanical interlock between the two wire segments, wherein the two wire segments are irregularly shaped and the space inside the tube is filled with solder or adhesive.
U.S. Pat. No. 6,544,197 (DeMello) also discloses a Nitinol tubing coupler, but additionally includes a safety wire in the joint to secure the two wire segments.
U.S. Pat. No. 6,918,882 (Skujins et al.) discloses a connector formed out of a nickel-chromium-molybdenum alloy, or a nickel-chromium-iron alloy, that is suitable for welding together the two wire segments.
None of the foregoing patents teach or suggest the novel composite guidewire disclosed herein, or the method for making the novel composite guidewire disclosed herein.
In addition to the foregoing, there are also many other types of wire-based surgical devices. By way of example but not limitation, these include other types of guidewires; snares; retrievers and graspers; embolic protection devices (e.g., filters); detachable devices that position embolic materials and implantable filters; biopsy devices; devices that deliver energy such as ultrasound, electric current, and radiofrequency; etc. These and other wire-based devices may require different performance characteristics along various segments of their length. By way of example but not limitation, a biopsy device might utilize a wire which requires the properties of titanium along one segment of the wire and the properties of a cobalt-chromium alloy along another segment of the wire. In fact, wire-based surgical devices frequently comprise multiple segments providing different functions, each of which might advantageously employ the differing properties of stainless steel, Nitinol, titanium, cobalt-chromium alloys, alloys based on the noble metals and various non-metallic composites.
Thus, in a further aspect of the present invention, the wire joining concepts of the present invention may be used to join different materials having desirable properties in a composite wire in order to achieve the performance characteristics desired for such other wire-based surgical devices.